The present invention is directed to an edge interference filter for an optical communication transmission in wavelength-multiplex. The edge interference filter has a layer sequence which is arranged between adjacent outer medias with the layer sequence being composed of alternately arranged layers with a high index of refraction and a low index of refraction with the two outer layers which are adjacent the outer media having the high index of refraction.
Filters of the species having a layer sequence of alternating layers of high and low index of refraction are known and examples are disclosed in an article by F. H. Mahlein, "A High Performance Edge Filter for Wavelength-Division Multi-Demultiplexer Units", Optics and Laser Technology, February 1981, pages 12-20. Under certain conditions, pairs of spectrally, complementary edge interference filters are required for optical communication transmission in wavelength-division multiplex. Such pairs in an unglued execution are known, for example, from a book by H. A. Macleod, Thin Film Optical Filters, Hilger, London, 1969, pages 111-153.
The theory of glued edge interference filters, such as mentioned in the article by Mahlein, show filters transmitting short-wave can be realized with a standard layer of material composed of SiO.sub.2 and TiO.sub.2 only for narrow interchannel spacings of about 40 nm given a wavelength of 1300 nm and a 20.degree. angle of incidence. Filters transmitting long waves can only be realized with greater interchannel spacings of about 120 nm given a wavelength of 1300 nm and a 20.degree. angle of incidence.
By contrast, edge interference filters transmitting long-wave for narrow interchannel spacing and filters transmitting short-wave for large interchannel spacings cannot be realized with the layer structures hitherto described.